With globalization of an application market of wireless communication systems, a variety of specifications have been demanded according to communication bandwidths proposed by each country. In recently established standards, a 3GPP LTE, IEEE 802.16, or IEEE 802.22 system determines specification such that standard air interface can be operated according to radio frequency environments of each country. Especially, under the condition that the systems should be operated over various frequency bandwidths, a scalable bandwidth is required for a basic control channel in the system. To detect a system synchronization signal and basic system information that are searched by a mobile station to access the system, the mobile station should be operated under various assumptions. Namely, if no consistent signal specification exists for one radio communication interface, the mobile station should attempt to perform reception and decoding for all combinations. This increases complexity of the mobile station. A 3GPP LTE system is designed such that the mobile station initially decodes system information in a minimum bandwidth. The 3GPP LTE system is designed to be operated in a minimum bandwidth of 1.25 MHz or 1.4 MHz. A channel search and decoding parts causing the complexity of the mobile station, that is, a synchronization channel and a primary broadcasting channel are designed to be suitable for the minimum system bandwidth. The mobile station performs search only in the minimum bandwidth. Even though the 3GPP LTE system uses any bandwidth within an entire 3GPP LTE bandwidth, since the search process is performed only for the minimum system bandwidth, development costs for the mobile station and complexity of the mobile station are reduced.
Such requirements are also necessary for IEEE 802.16m. In a current legacy system, a system bandwidth is fixed at 10 MHz. IEEE 802.16m, which improves a legacy system of IEEE 802.16, defines 5 MHz to 20 MHz or more as a basic system bandwidth and is required to support the legacy system.
Since a minimum value of the system bandwidth in IEEE 802.16m is 5 MHz or less, the system should be designed so as to operate in such a minimum bandwidth. If a wider bandwidth should be supported, a structure which can easily be extended to support a broader bandwidth is necessary. Furthermore, a legacy support at 10 MHz should be considered.
FIG. 1 illustrates an example of a synchronization channel structure of a 3GPP LTE system.
A synchronization channel (SCH) used in the 3GPP LTE system sets a primary SCH (P-SCH) and a secondary SCH (S-SCH) in a minimum bandwidth at regular intervals within a radio frame. The P-SCH is carried on orthogonal frequency-division multiplexing (OFDM) at intervals of two subcarriers and transmitted. The S-SCH is constructed in an overlap format of two short codes set at intervals of two subcarriers. One of the two short codes is shifted by one subcarrier. To discriminate a start location from a radio frame, the first S-SCH and the second S-SCH have different structures.
FIG. 2 illustrates an example of a synchronization channel structure of an IEEE 802.16 system.
In an IEEE 802.16e (WiMAX) system, a preamble for a SCH is designed to occupy an entire system bandwidth. Preamble sequences are inserted at intervals of three OFDM subcarriers. Here, a preamble for a SCH is denoted by ‘SCH’ for unitary.
In FIG. 2, since offset can be assigned as 0, 1, and 2, three discernible codes may be transmitted. The offset is actually associated with a sector. When system bandwidth varies, the preamble sequences are separately defined to be suitable for the bandwidth. In the 3GPP LTE, SCHs are generated twice within one wireless frame. The SCHs are set at intervals of 5 ms, whereas a preamble of the IEEE 802.16e (WiMAX) is transmitted in units of a 5 ms frame. Accordingly, the preamble is transmitted at a rate as in the 3GPP LTE.
IEEE 802.16m is designed to be an improved version of IEEE 802.16e and has been developed to satisfy IMT-Advance performance requirements. However, the current IEEE 802.16e can not efficiently support a scalable bandwidth and has a disadvantage in detecting a system signal by the mobile station. The preamble sequence of IEEE 802.16e is constructed at three unit intervals but uses different subcarrier offset locations per sector. If signals according to sectors are overlapped, repeated features of the preamble are eliminated. Then repeated patterns at a cell edge in the time domain can not be discerned.
Consequently, in an air interface specification of the current IEEE 802.16e, the mobile station should perform preamble search corresponding to an entire system bandwidth and cannot efficiently perform sequence search at a cell edge.